Hello
![Smiley :)](https://forum.avast.com/Smileys/default/smiley.gif)
Are you running another AV with avast?
Have you ever had another AV installed and if so what and how did you remove it?
Please try repairing avast! installation: Go to Control Panel > Add/Remove programs > avast! antivirus > Remove
Then choose Repair function in the pop up window (Repair) (you need to be online to do the repair)
![Wink ;)](https://forum.avast.com/Smileys/default/wink.gif)
And then try a boot-time scan.
If that doesn't work try, uninstall, reboot, install, reboot.